The teachings herein relate generally to techniques for compensation of changes in power generator speeds.
Power generation systems utilize various sources to generate electrical power, such as hydropower, combustion of fuels such as coal, oil and gas, and wind power. Typically, these sources are harnessed to rotate turbines that are coupled to power generators, which are in turn coupled to various loads via, for example, a power distribution grid (hereinafter referred to as a “grid”).
Generation systems utilize power generators that generally produce electrical power that is proportional in frequency to the rotational speed of a turbine. Thus, changes in turbine speeds may result in changes to the power frequency generated. Accordingly, the rotational speed of the turbine should be regulated to produce a frequency that matches the requirements of the grid. In situations where the turbine speed has been changed relative to the required speed, or is not sufficient to produce the required frequency, measures must be taken to modulate the frequency outputted by the generator to match the grid frequency.
A number of the prior art techniques for modulating output include controlling mechanical variables such as fuel flow rate to regulate revolution speed, and various power conversion schemes, which are either slow and/or inefficient.
Techniques for varying turbine power while maintaining desired frequency output have been used, although these techniques generally require the use of multi-shaft configurations, or power converters coupled to the output of the generation system.
Furthermore, doubly fed induction generators have been used in conjunction with wind turbines for reactive power control in response to fluctuations in wind speed. Also, some wind turbine systems use power converters to adjust output to match the grid frequency. However, such reactive techniques do not provide a method for maintaining a selected frequency output during modifications to turbine speed (e.g., to increase efficiency), such as during turbine turn-down or modifications of turbine speed, e.g., in response to power demands.
Accordingly, there is a need for a system and method for modulating power output and frequency for a power generation unit that allows the speed of the power generation unit to be modified without disturbing output power, e.g., to allow turbines in the generation unit to be turned-down or otherwise modified without disrupting the frequency output of the power generation unit.